Discussion on the mechanism leading to positive synergism in SF6 mixtures with HFO1234ze(E)

Abstract

The electric strength in HFO1234ze(E)/SF6 mixtures is investigated with swarm and breakdown experiments. The density-reduced critical electric field as well as the breakdown voltage measured with both techniques, are found to be higher than that of the pure gases in mixtures with more than 10% SF6. The underlying mechanism for the observed positive synergy is investigated and the explanation proposed by Hunter and Christophorou (1985 J. Appl. Phys. 57 4377-85) is discussed for this mixture. The pressure-dependent attachment rate is found to increase with SF6 ratio thus satisfying the main requirement of the proposed mechanism in Hunter and Christophorou's study. It appears nevertheless that due to the fast saturation with pressure and low rates in the mixtures, the three-body attachment processes account only for a small increase in the electric strength. An alternative hypothesis is proposed which considers the strong reduction of electron energies via inelastic processes in HFO1234ze(E), and is qualitatively demonstrated based on measurements and simulations.